Perusal of the Subaru web pages came up with the owner's manual for the 2011 model year here Subaru Tribeca Service Schedules and Owners' Manuals
I dug through the manual and the only place they reference towing the vehicle is in section 9 on page 9-14 (Page 319) of the pdf.
Also on page 9-18 (Page 323) they say
"The traveling speed must be limited to less than 20 mph (30
km/h) and the traveling distance to less than 31 miles (50 km). For
greater speeds and distances, transport your vehicle on a flatbed
Not looking too good for 4 down towing, boss.
All else fails call your local Subaru dealer.
They do make some great cars.
Chris in Virginia
2006 Sunseeker 3100SS/LTD
2008 Smart Passion Cabriolet TOAD
1986 Honda Helix (Original owner)